3 Answers
3

Ubuntu 12.04 LTS and later

Administrators are added to the sudo group, but the admin group is supported for backward compatibility. From the release notes:

Up until Ubuntu 11.10, administrator access using the sudo tool was granted via the admin Unix group. In Ubuntu 12.04, administrator access will be granted via the sudo group. This makes Ubuntu more consistent with the upstream implementation and Debian. For compatibility purposes, the admin group will continue to provide sudo/administrator access in 12.04.

It is not created when you do a fresh install, though it is still present if you upgraded from previous distributions. Either way, the admin group appears in the /etc/sudoers file.

Ubuntu 11.10 and earlier

the user created during installation belongs to admin group, not sudo;

no guide or manual I ever read advices to use the sudo group;

no one feels the need to use the sudo group, because the admin group can do all one needs.

Conversely, on Debian the group enabled in /etc/sudoers is the sudo group, and there is no admin group. But the user created during installation is not put in that group, because Debian has the root account enabled. You should do it explicitly, if you want to.

Also, Fedora is similar to Debian, having root enabled and no default privileges for the user create during installation. But the administrative group configured in /etc/sudoers is the more traditional group wheel.

In conclusion, I think there is no use for sudo group in Ubuntu, simply it is a Debian heritage.

On my Ubuntu system, no users are member of sudo: grep '^sudo:' /etc/group (just installed). Not sure about Debian, I've just added my own name to the /etc/sudoers file.
–
LekensteynMay 17 '11 at 15:59

1

@Lekensteyn: as I said, on Debian you should explicitly add a user to the sudo group to gain administrative privileges: su -c "gpasswd -a $USER sudo", no need to modify /etc/sudoers. Or you can stand with the Debian way of using directly the root account.
–
enzotibMay 17 '11 at 16:03